This invention relates generally to mechanical shift, pneumatic assist pilot valves for diaphragm pumps and the like and more particularly to a lost motion device for stabilizing the mechanical shift of such valves.
U.S. Pat. No. 4,854,832 issued to Richard K. Gardner (co-inventor herein) and Nicholas Kozumplik Jr. and assigned to The Aro Corporation (common Assignee herein) discloses a mechanical shift, pneumatic assist pilot valve for use in diaphragm pumps. Briefly that invention comprises a combined mechanical shifting mechanism and pneumatic pilot valve construction to control the cycling of a double diaphragm pump. The mechanical cycling or shifting mechanism is positioned between pressure chambers of the diaphragm pump in the pump housing and extends axially into one or the other pressure chamber.
The shifting mechanism moves axially in response to engagement by one of the pump diaphragms. Upon engagement by a diaphragm, the mechanical shift opens fluid pressure passageways to a pneumatic pilot valve which controls fluid flow to the respective pressure chambers associated with the diaphragm pump. A positive pilot signal is thus supplied through the entire stroke or cycle of the diaphragm pump. The mechanical shifting mechanism is not connected directly to a diaphragm or to the connecting rod which connects the diaphragms.
In the operation of diaphragm pumps it is not uncommon to have air drawn into the fluid chamber of the pump along with the pumped fluid. The air is compressed during the pumping of the fluid and during shifting of the air valve may expand to cause the diaphragm to back up slightly. Due to the pump dynamics, fluid pressure may also be momentarily higher than air pressure. This allows the pilot rod to also back up and shut the signal off to shift the main valve. This may cause the pump to stutter and in some instances stop or stall.
The foregoing illustrates limitations known to exist in present devices and methods. Thus it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly a suitable alternative is provided including features more fully disclosed hereinafter.